(1) The present invention relates to the manufacture of unground bearings. Specifically, this invention is directed to an improved unground ball bearing.
(2) Description of the Prior Art
Unground bearings are generally well known and are used in many applications. This type of bearing is less expensive to produce when compared to ground bearings in which the inner and outer races are precision machined. However, unground bearings produce a relatively high degree of noise and more wobbling due to the low manufacturing tolerances.
A major disadvantage with prior unground ball bearings is their short life span. This short life span is in part due to the fact that the manufacture of the typical unground bearing includes a crimping operation wherein a peripheral edge portion of the outer race defining member is bent over the inner race defining member to retain the inner race and the bearings within the outer race. This crimping operation cannot be performed on a heat treated part because such a heat treated race would distort during crimping. Accordingly, prior art practice has been to heat treat the entirely assembled bearing, which results in an uneven hardness of the metal comprising the bearing races. This uneven hardness occurs between those areas of the inner and outer races in contact with the balls and those areas not in contact with the balls during heat treating. The reason for this uneven hardness is that the balls conduct some of the heat away from the races. Thus, the races will wear unevenly which increases the noise and wobbling.
Another disadvantage with prior unground ball bearings, which also results from the heat treatment of the assembled bearing, is the scaling of the inner surfaces of the races. This scaling results from the heat treating of the metal. With the ball bearings being fully assembled, removal of this scale is inhibited and thus the wear of the ball bearing is increased by the friction caused by the scale.
As noted above, the heat treatment of previously produced unground ball bearings, particularly bearings of small size such as employed in roller skates, had to be performed after full assembly since the side wall of the outer race would have bowed outwardly if it was crimped around the inner race after being hardened. A straight outer race wall is mandatory for most bearing applications.
Furthermore, the previously used method of assembling unground ball bearings resulted in lost balls. Typically, the balls were first positioned between the inner and outer races and then the outer race would be crimped over the inner race. During the crimping operation, balls would fall out from between the races thereby resulting in a defective product. The noise level and resulting wobbling would be dramatically increased in a bearing which did not possess the proper quantity of balls.